1. Field of the Invention
The present invention relates to an ink-jet head that discharges ink droplets toward a recording medium to perform printing thereon.
2. Description of the Related Art
In an ink-jet head which is used in an ink-jet printer or the like, ink that is supplied from an ink tank is distributed to a plurality of pressure chambers and pulse pressures are selectively applied to the individual pressure chambers, whereby ink droplets are discharged from nozzles. One means for selectively applying pressures to the pressure chambers is an actuator unit having a lamination of a plurality of piezoelectric sheets made of piezoelectric ceramics.
Among the conventional ink-jet heads of the above kind is one having one actuator unit in which a plurality of continuous flat plates as piezoelectric sheets that cover a plurality of pressure chambers are laminated on each other and at least one of those piezoelectric sheets is interposed between a common electrode that is common to many pressure chambers and is kept at the ground potential and many individual electrodes (drive electrodes) that are opposed to the respective pressure chambers (refer to JP-A-4-341852 (FIG. 1)). If an individual electrode corresponding to a certain portion of the piezoelectric sheet that is interposed between the individual electrode and the common electrode and polarized in the lamination direction is given a potential that is different than the common electrode, that portion expands or contracts in the longitudinal direction due to what is called the piezoelectric longitudinal effect because an external electric field develops there in the polarization direction of the piezoelectric sheet. In this case, the portion of the piezoelectric sheet interposed between the individual electrode and the common electrode serves as an active layer that is deformed according to the piezoelectric effect because of the development of the external electric field. As a result, the capacity of the associated pressure chamber is varied and an ink droplet is discharged toward a recording medium from a nozzle that communicates with the pressure chamber.